To have the value refer to the last full capacity instead of the design capacity of the battery, add in your .i3status.conf:

last_full_capacity = true


order += "volume master"

volume master {
#	format = " ♪: %volume  " 
	device = "default"
	mixer = "Master"
	mixer_idx = 0
	# termsyn font
	format = "À %volume "
}
